Combine pudding and milk and beat until thick.,Fold in Cool Whip.,Layer bottom of a 9 x 13-inch pan with graham crackers. Add layer of pudding mix.,Continue adding layers of graham crackers and pudding mix, but stop with graham crackers on top. Bring cocoa, evaporated milk and sugar to a boil, stirring constantly.,Let cool for 1 minute, then add margarine and vanilla flavoring.,Pour over cake.,______